The present invention relates to a method of hydroponic culture in which plants are grown while a nutrient solution is continuously circulated within a culture tank. The invention provides a method of accelerating the growth of plants and increasing the yield by leaps and bounds.
What should be mentioned first is that the high rate of growth and high yield achieved by the method of the present invention are much greater than those achieved by the usual soil culture and hydroponic culture which have heretofore been practiced in various ways.
Generally, in soil culture, the growth of plants is governed by a combination of many environmental factors, such as the amount of sunshine, temperature, CO.sub.2 concentration, wind velocity, humidity, the proportion and concentration of fertilizer, and the nature, water content and pH of soil. Further, whether the growth of plants is good or bad is determined by the complex physiological mechanism of plants as the ground and underground environments for growth of plants are organically interrelated. In reality, however, the study of the underground environment of the roots of plants is not yet sufficient and the underground environment cannot be freely controlled. Therefore, it may be said that the organic control of the ground and underground environments, or the overall environment, of plants is impossible at present. The trend of growth of plants which we believe we have a general knowledge of is, in fact, the result of our observation of the growth of plants carried out under conditions greatly limited by insufficient environment for the growth of plants or under conditions where the substance producing inherent ability of plants has not yet been fully developed. However, this important fact has not yet been fully understood and, therefore, there is apt to be a mistaken belief that there is no possibility of accelerating the growth of plants by leaps and bounds.
Even if the full control of said environment for growth of plants is impossible, it is not impossible to bring about a surprising result of growth if those of the various environmental factors affecting the growth of plants which are governing factors, and their mutual actions affecting the growth of plants are clarified to the extent that the governing factors can be improved or controlled.
Now, the problem is what factors are important. In this connection, I have conducted various tests on hydroponic culture and found that the controlled flow rate of nutrient solutions and controlled liquid level with respect to the roots of plants are very important factors throughout the overall period of growth of plants. This means that it is important to make a series of coordinated controlled supplies of a nutrient solution in association with the development of the growing roots and ground portions throughout the overall period of culture extending from germination to harvest rather than giving good environment in a single period or fragmentarily in the course of growth of plants, thereby maintaining such a condition as will allow the roots to develop their functions to the fullest extent.
Plants absorb oxygen, water and nutrients from their roots and send them to the stalks and leaves in the ground region to effect photosynthesis in the ground region by using solar energy and oxygen monoxide. If, however, water necessary for physiological purposes, nutrients necessary for growth and oxygen necessary for respiration of root cells which affects the water and nutrient absorbing function cannot be sufficiently taken in, then the growth of plants cannot but be limited since the absorption of water and nutrients is insufficient even if there is sufficient sunlight in the ground region. This means that usually, almost all plants which seem to be favorably growing are, in fact, under many limitations described above and that, as a result, the efficiency of utilization of solar energy is very low.
On the other hand, the amount of all substance in a plant at any instant is the cumulative amount of growth of the plant at that instant, while the amount of growth at any instant is dependent on the growth ability at an instant just before that instant. In other words, it may be said that growth brings about growth. Therefore, the degradation of the root system, i.e., the lowering of the physiological activity, results in a rate-determining factor which degrades the subsequent growth.